1. Field of the Invention
The field of the invention relates to organic material and especially to equipment for densifying this material, particularly pelletizing the material to put it into a form faciliating its use. The invention is particularly adapted to bio mass materials, but is not limited thereto being adapted to the pelletizing of other materials such as human and animal food products.
2. Description of the Prior Art
The invention involves, particularly, improvements in machinery for densifying and pelletizing bio mass material. Accordingly background in that area is provided.
The nature and source of organic materials suitable as sources of fuel are well known in the art, this being elucidated in patents such as U.S. Pat. Nos. 3,227,530; 3,492,131; and, 4,015,951. Apparatus or machines for pelletizing bio mass material generally follow a typical type of construction such as that shown in FIGS. 2-5 of U.S. Pat. No. 4,211,740. Typically the known pelletizing mills are of a rotary construction wherein a rotary die or dies rotate within a cylindrical housing or drum to compact and densify the bio mass material, the process involving changing the direction of flow of the bio mass material through 90.degree. to force it through orifice plates in which the pellets are formed.
In general the object or goal involved in the handling and pelletizing of bio mass material is to realize practical moisture removal, to place the material in a form adapted for economical transportation and purported cell fracture to allow better combustion in solid form or when pulverized for combustion in suspension.
The present state of the art as shown presents multiple problems. As indicated in the foregoing the typical type of apparatus utilized for densification and pelletizing consists of a rotary die which rotates relative to rollers which are supplied with pulverized bio mass material which is forced through a series of holes or orifices results in extruded densified pellets. The process as utilized has evolved from a system and apparatus long used for the pelletizing of food and feed products. The adaptation of this known apparatus and process for fuel production has effected and resulted in little change in the machine beyond strenthing gears, shafts, shear pins, etc., to withstand the great pressure and friction consistent with bio mass which product does not have the inherent natural lubricants of feed and food products and is subject to higher pressure required to produce a satisfactory fuel. The leading edge of technology available is perhaps the machine known as C.P.M. 8000, but even at the leading edge of the technology there are present serious shortcomings affecting the economic practicality of producing a satisfactory marketable fuel, the shortcomings being present particularly because of energy considerations as pointed out hereinafter.
The following points out principal drawbacks and deficiencies inherently present with respect to the present state of the art.
A particular deficiency with respect to known apparatus has to do with electrical energy requirements. There can be considered a machine of the type as identified in the foregoing having a main driving motor of 500 H.P., drawing 600 amperes which can produce at the rate of from 51/2 to 10 tons per hour of densified pellets. A computation of the amperage, that is, current draw per hour in relation to the resulting production of fuel in tons will indicate an electrical energy cost per ton in proportion to the BTU recoverable energy at the time of combustion such that the energy relationships make the process almost, if not economically not practicable.
Another draw-back involved with respect to the conventional machinery is the original capital cost. For example, the rotary die may weigh 800 pounds and must be revolved or spun at a speed of 900 RPM. This necessitates a very heavy and costly gear train to reduce the 1700 RPM of the 500 H.P. motor to the slow die speed. The speed reduction itself results in an energy loss.
A further drawback to the conventional machinery involves the costs of replacing expendable parts. Typically there is an unacceptable die and roller shell replacement cost related to economic working life produced by bio mass friction involved in the flow direction change of the bio mass material and the unfavorable attitude of introduction of bio mass material in the densification chambers. This physical circumstance has been disclosed by careful examination of the machinery and die sections after use. There is an undesirable physical flow pattern that takes place that operates to destroy dies and rollers much too fast and which circumstance also consumes an inordinate amount of electrical energy manifested by the kinetic energy developed which is transformed into heat resulting in saturated steam released by the pellets after passing through the die. This heat is an unacceptable costly form of thermal energy which in its electrical energy form is even greater than the resistance heat.
Another factor is that of bio mass moisture requirement. Experience in the field has revealed that the moisture content of the bio mass for processing in existing systems is too limited for optimum economic production of fuel pellets in the range of 12% to 13% of moisture as required resulting in balance of plant operation dictated by pellet machine moisture requirements.
Typical prior art machines as identified in the foregoing involve substantial production down time due to the necessity to replace dies, adjust rollers, etc. To produce a satisfactory quality in the pelletized fuel, roll adjustment is necessary. This adjustment is slow, difficult and dangerous. If not done on a timely basis and if not done correctly the result will be an unsatisfactory pellet or a gross reduction in die and roller economic life.
The introduction of raw material into the pelletizing apparatus is extremely important and critical. The required pressure for a satisfactory densification of bio mass as indicated in the foregoing has required the use of massive rollers and a reinforced die plus an extra roller to partially distribute forces generated in an attempt to alleviate the flexing of the die. This significantly complicates the even distribution of the raw material across the face of the die resulting in uneven extrusion of pellets, causing power loss related to production volume and shortens die and roller economic life. The physics involved in trying to feed a round spinning die evenly and to equally feed two or more rollers is at best very difficult as is evidenced by the variety of feed mechanisms and "plows" that have been experimented with in the past.
The metallurgy of the parts involved in the apparatus is extremely significant. Metals have been developed for the glass industry as well as other processes that could far better withstand the abrasiveness of bio mass material. However, to date it has not been economically praticable to cast these materials and machine them for application in presently known pelletizing systems. This has dictated selection of raw material more critically then would be desireable if the die and rollers could be fabricated from a material that would withstand more abrasive raw material without increasing replacement of parts, require more critical moisture control or increase energy requirements.
The herein invention, an exemplary form of which is described in detail hereinafter seeks to make available densifying equipment for bio mass or other material constructed in accordance with unique concepts so as to overcome all of the above identified drawbacks and deficiencies of the prior art. The objectives to be attained by the herein invention are identified with particularity hereinafter.